High-temperature-resistant foam ceramic wave-absorbing material and preparation method thereof

Abstract

This invention relates to a high-temperature resistant foam ceramic microwave absorbing material and its preparation method, belonging to the technical field of microwave absorbing stealth materials. The preparation method of the high-temperature resistant foam ceramic microwave absorbing material includes the following steps: (1) mixing silicon carbide and calcium carbonate into a mixed powder; (2) mixing the mixed powder, borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose, and water to form a slurry; (3) impregnating a foam ceramic component with the slurry, followed by drying and sintering to obtain the high-temperature resistant foam ceramic microwave absorbing material. The foam ceramic microwave absorbing material prepared by this invention retains the original properties of the foam ceramic to the maximum extent, and exhibits excellent microwave absorption performance, especially since high temperature of 850℃ has no effect on its microwave absorption performance, indicating that the foam ceramic microwave absorbing material prepared by this invention has excellent microwave absorption performance and high-temperature resistance.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing stealth materials technology, specifically relating to a high-temperature resistant foam ceramic microwave absorbing material and its preparation method. Background Technology

[0002] Microwave-absorbing materials are an important type of structural functional material. With the increasing demands on the performance of microwave-absorbing materials in fields such as radar stealth, electromagnetic shielding, communication anti-interference, information leakage prevention, and radiation protection of military facilities, multi-functionality has become a key development direction for microwave-absorbing materials. In particular, structural microwave-absorbing materials are required to not only have excellent electromagnetic wave absorption performance, but also meet the requirements of being lightweight, waterproof, temperature resistant, and load-bearing.

[0003] Polymer absorbing materials are simple to mold and easy to use, but they have drawbacks such as easy aging, poor temperature resistance, and short lifespan, which cannot meet the multifunctional requirements of absorbing materials. Ceramic absorbing materials have become a research focus of high-temperature absorbing materials due to their excellent temperature resistance, but they also have problems such as complex preparation processes and difficult molding, especially in terms of performance, such as heavy weight and poor impact resistance.

[0004] Foam ceramics, with their advantages of being lightweight, heat-insulating, waterproof, and fireproof, perfectly meet the multifunctional requirements of structural microwave absorbing materials. Therefore, some scholars have proposed "introducing microwave absorbing agents into foam ceramics" to prepare high-performance / multifunctional foam ceramic microwave absorbing materials. However, the firing temperature of foam ceramics is about 1200℃. Since the internal pores of the fired foam ceramics are independent and closed, it is impossible to introduce microwave absorbing agents into them. Therefore, the operation of "introducing microwave absorbing agents into foam ceramics" can only be placed before the sintering process of foam ceramics, that is, in the raw material preparation stage. This means that the microwave absorbing agent must be sintered at a high temperature of 1200℃ along with the raw materials. This operation has two problems: (1) Adding microwave absorbing agents will change the ratio of raw materials and reduce the foaming performance of foam ceramics. The ratio of raw materials and the sintering process must be fully adjusted, which makes the preparation process of foam ceramics more complicated; (2) The microwave absorbing agent will be severely oxidized during high-temperature sintering, resulting in poor microwave absorbing performance of the prepared foam ceramics. Summary of the Invention

[0005] This invention addresses the problems of complex processes and poor absorption performance of foam ceramic absorbing materials prepared by the prior art, and provides a high-temperature resistant foam ceramic absorbing material and its preparation method.

[0006] The specific technical solution is as follows:

[0007] The first objective of this invention is to provide a method for preparing high-temperature resistant foam ceramic microwave absorbing material, comprising the following steps:

[0008] (1) Mix silicon carbide powder and calcium carbonate powder evenly to make a mixed powder;

[0009] (2) Mix the mixed powder obtained in step (1), borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose and water, stir evenly to make a slurry;

[0010] (3) Immerse the foam ceramic component made from commercially available foam ceramic in the slurry obtained in step (2), draw a vacuum to reduce the air pressure on the surface of the slurry, and then restore the air pressure on the surface of the slurry to normal pressure.

[0011] (4) Take out the foam ceramic component obtained in step (3) and place it in an oven to dry;

[0012] (5) Take out the foam ceramic component obtained in step (4) and place it in a high-temperature furnace for sintering to obtain the high-temperature resistant foam ceramic microwave absorbing material.

[0013] The effects of adopting the above technical solution are:

[0014] Silicon carbide in the mixed powder is an excellent high-temperature microwave absorber. It is dispersed in the openings on the surface of the foam ceramic component to form a spatial grid structure, which enables the foam ceramic component to have excellent electromagnetic wave absorption performance.

[0015] During high-temperature sintering, borax, sodium silicate and potassium carbonate form a continuous and viscous molten phase, which on the one hand encapsulates the silicon carbide particles, and on the other hand seals the carbon dioxide decomposed by calcium carbonate, thereby further preventing the oxidation of silicon carbide particles.

[0016] During high-temperature sintering, the carbon dioxide produced by the decomposition of calcium carbonate causes the molten phase to foam. The foaming of the molten phase expands the spatial distribution range of silicon carbide particles in the openings on the surface of the foam ceramic component, thereby further improving the electromagnetic wave absorption performance of the foam ceramic component.

[0017] Polyvinyl alcohol is added to adjust the plasticity and viscosity of the slurry, increase the amount of slurry entering the openings on the surface of the foam ceramic component, and at the same time ensure that the slurry that has entered the openings on the surface of the foam ceramic component does not flow out during subsequent operations.

[0018] Sodium carboxymethyl cellulose is added to improve the uniformity and stability of the slurry and to prevent the slurry from separating or settling.

[0019] Furthermore, in step (1), the weight ratio of silicon carbide powder to calcium carbonate powder is 1:(1.5~2.2).

[0020] Furthermore, in step (1), the average particle size of silicon carbide powder is 10-20 μm, and the average particle size of calcium carbonate powder is 5-10 μm.

[0021] Furthermore, in step (2), the weight ratio of the mixed powder, borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose and water is (5.3-7.9):(1.2-1.4):(14-16):(1.2-1.5):(0.2-0.3):(0.3-0.5):100.

[0022] Furthermore, in step (3), vacuuming is performed to reduce the air pressure on the surface of the slurry to 0.71 to 0.79 standard atmospheres and maintain this pressure for 9 to 13 minutes.

[0023] Furthermore, in step (3), the air pressure on the surface of the slurry is restored to normal pressure and maintained for 3 to 5 minutes.

[0024] Furthermore, in step (4), during the drying process, the temperature is maintained at 85-90℃ for 120-150 minutes.

[0025] Furthermore, in step (5), during the sintering process, the sintering temperature is 935–950℃ for 16–19 min.

[0026] The effect of adopting the above technical solution is that during the sintering process, when the temperature rises above 700℃, the calcium carbonate in the mixed powder will decompose to generate carbon dioxide, which will prevent the silicon carbide particles from contacting oxygen and avoid oxidation of the silicon carbide particles.

[0027] The second objective of this invention is to provide a high-temperature resistant foam ceramic microwave absorbing material, which is prepared using the method described above.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The foam ceramic microwave absorbing material of the present invention is based on the modification of commercially available foam ceramics. The sintering temperature of commercially available foam ceramics is generally around 1200℃. The sintering temperature used in the present invention is 935~950℃, which is much lower than the sintering temperature of commercially available foam ceramics. It will not affect the intrinsic physical and mechanical properties of commercially available foam ceramics.

[0030] (2) Compared with commercially available foam ceramics, the foam ceramic absorbing material of the present invention is only different in surface pore morphology, and the internal pore structure is exactly the same. Therefore, the foam ceramic absorbing material of the present invention also has the properties of being lightweight, heat-insulating, waterproof, temperature-resistant, and impact-resistant.

[0031] (3) The borax, sodium silicate and potassium carbonate in the slurry of the present invention are in a molten state at 935 to 950°C, but are in a solid state below 850°C. Therefore, in actual use, when the temperature does not exceed 850°C, the solid ceramic matrix formed by introducing the slurry and sintering at high temperature will prevent the oxidation of the silicon carbide particles inside it. This means that the maximum operating temperature of the foam ceramic microwave absorbing material of the present invention is 850°C. Attached Figure Description

[0032] Figure 1 This is a process flow diagram for preparing the high-temperature resistant foam ceramic microwave absorbing material of the present invention;

[0033] Figure 2 This is an optical macroscopic photograph of commercially available foam ceramics used in embodiments of the present invention. Detailed Implementation

[0034] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0035] For ease of description and performance comparison, the commercially available foam ceramics used in the following four examples are all of the same specifications and dimensions, and have undergone surface cleaning and drying treatment. The commercially available foam ceramics used were sintered at 1220℃, and have a compressive strength of 6.9 MPa and a density of 0.49 g / cm³. 3 The average aperture is 1.8 mm, the total porosity is 80%, the closed-pore rate is 73%, and the optical macromorphology is as follows: Figure 2 As shown.

[0036] Example 1

[0037] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material, comprising the following steps:

[0038] (1) Mix silicon carbide powder with an average particle size of 10 μm and calcium carbonate powder with an average particle size of 5 μm at a weight ratio of 1:1.5 to prepare a mixed powder.

[0039] (2) The mixed powder obtained in step (1), borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose and water are mixed in a weight ratio of 5.3:1.2:14:1.2:0.2:0.3:100 and stirred evenly to make a slurry;

[0040] (3) Immerse the component made of commercially available foam ceramic in the slurry obtained in step (2), vacuum the slurry surface pressure to 0.71 standard atmospheres, maintain for 9 minutes, and then restore the slurry surface pressure to normal pressure and maintain for 3 minutes.

[0041] (4) Take out the foam ceramic component obtained in step (3) and place it in an oven to dry at 85°C for 150 minutes;

[0042] (5) Take out the foam ceramic component obtained in step (4) and place it in a high-temperature furnace. Sinter at 935°C for 19 minutes to obtain the high-temperature resistant foam ceramic microwave absorbing material.

[0043] Example 2

[0044] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material, comprising the following steps:

[0045] (1) Silicon carbide powder with an average particle size of 12 μm and calcium carbonate powder with an average particle size of 6 μm are mixed evenly at a weight ratio of 1:1.7 to prepare a mixed powder.

[0046] (2) The mixed powder obtained in step (1), borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose and water are mixed in a weight ratio of 6.1:1.3:15:1.3:0.2:0.4:100 and stirred evenly to make a slurry;

[0047] (3) Immerse the component made of commercially available foam ceramic in the slurry obtained in step (2), and vacuum the slurry surface pressure to 0.74 standard atmospheres for 10 minutes. Then restore the slurry surface pressure to normal pressure and maintain it for 4 minutes.

[0048] (4) Take out the foam ceramic component obtained in step (3) and place it in an oven to dry at 85°C for 150 minutes;

[0049] (5) Take out the foam ceramic component obtained in step (4) and place it in a high-temperature furnace. Sinter at 940°C for 18 minutes to obtain the high-temperature resistant foam ceramic microwave absorbing material.

[0050] Example 3

[0051] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material, comprising the following steps:

[0052] (1) Silicon carbide powder with an average particle size of 15 μm and calcium carbonate powder with an average particle size of 8 μm are mixed evenly at a weight ratio of 1:1.9 to prepare a mixed powder.

[0053] (2) The mixed powder obtained in step (1), borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose and water are mixed in a weight ratio of 7.0:1.3:15:1.4:0.3:0.4:100 and stirred evenly to make a slurry;

[0054] (3) Immerse the component made of commercially available foam ceramic in the slurry obtained in step (2), and vacuum the slurry surface pressure to 0.76 standard atmospheres for 12 minutes. Then restore the slurry surface pressure to normal pressure and hold for 4 minutes.

[0055] (4) Take out the foam ceramic component obtained in step (3) and place it in an oven. Keep it at 90°C for 120 minutes to dry it.

[0056] (5) Take out the foam ceramic component obtained in step (4) and place it in a high-temperature furnace. Sinter at 945°C for 17 minutes to obtain the high-temperature resistant foam ceramic microwave absorbing material.

[0057] Example 4

[0058] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material, comprising the following steps:

[0059] (1) Silicon carbide powder with an average particle size of 20 μm and calcium carbonate powder with an average particle size of 10 μm are mixed evenly at a weight ratio of 1:2.2 to prepare a mixed powder.

[0060] (2) The mixed powder obtained in step (1), borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose and water are mixed in a weight ratio of 7.9:1.4:16:1.5:0.3:0.5:100 and stirred evenly to make a slurry;

[0061] (3) Immerse the component made of commercially available foam ceramic in the slurry obtained in step (2), and vacuum the slurry surface pressure to 0.79 standard atmospheres for 13 minutes. Then restore the slurry surface pressure to normal pressure and maintain it for 5 minutes.

[0062] (4) Take out the foam ceramic component obtained in step (3) and place it in an oven. Keep it at 90°C for 120 minutes to dry it.

[0063] (5) Take out the foam ceramic component obtained in step (4) and place it in a high-temperature furnace. Sinter at 950°C for 16 minutes to obtain the high-temperature resistant foam ceramic microwave absorbing material.

[0064] Test method description:

[0065] The performance of the foam ceramic microwave absorbing materials prepared in Examples 1-4 was tested. The compressive strength and density were measured according to the national standard GB / T 5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products"; the total porosity and closed-cell ratio were measured using the indirect Archimedes' displacement method; the microwave absorption performance was evaluated by testing the reflectivity of the samples against electromagnetic waves of 8–18 GHz using the bow-shaped reflectivity test principle. Lower reflectivity indicates better microwave absorption performance.

[0066] The physical and mechanical properties of the foam ceramic absorbing materials prepared in Examples 1-4 and the original foam ceramics are shown in Table 1.

[0067] Table 1. Physical and mechanical properties of the foam ceramic absorbing materials prepared in Examples 1-4 and the original foam ceramics.

[0068]

[0069] As shown in Table 1, because the preparation method described in this invention introduces slurry into the original foam ceramic, it transforms into a new ceramic matrix after high-temperature sintering. Compared to the original foam ceramic, the density of the foam ceramic microwave absorbing materials prepared in Examples 1-4 increases to 0.51–0.53 g / cm³. 3 The total porosity decreased to 77-78%, and the increased density further led to an increase in compressive strength to 7.0-7.3 MPa. In addition, the introduction of slurry would seal some of the open pores on the surface of the original foam ceramic, turning it into closed pores. Therefore, although the total porosity of the foam ceramics prepared in Examples 1-4 was reduced, the closed pore rate actually increased slightly to 74-75%.

[0070] Table 2 shows the reflectivity of the foam ceramic absorbing materials prepared in Examples 1-4, the original foam ceramic, and the materials after being kept at 850℃ for 10 hours.

[0071] Table 2. Reflectivity of the foam ceramics prepared in Examples 1-4 and the original foam ceramics

[0072]

[0073] As shown in Table 2, the lowest reflectance of the original foam ceramic was as high as -0.04dB, and the average reflectance was as high as -0.02dB. After being kept at 850℃ for 10h, the lowest and average reflectance of the original foam ceramic did not change, indicating that the high-temperature heat treatment had no effect on the microwave absorption performance of the original foam ceramic.

[0074] For the foam ceramic absorbing materials prepared in Examples 1-4, the minimum and average reflectance values ​​were as low as -23.1 to -20.6 dB and -15.2 to -13.8 dB, respectively. After being kept at 850 °C for 10 h, the minimum and average reflectance values ​​increased slightly to -22.9 to -20.5 dB and -15.0 to -13.7 dB, respectively. Obviously, the increase in both values ​​was very small, indicating that the foam ceramic absorbing material prepared in this invention has excellent wave absorption performance and high temperature resistance.

[0075] Furthermore, considering the assertion that "high-temperature heat treatment has no effect on the microwave absorption performance of the original foam ceramic," it indicates that the excellent microwave absorption performance of the foam ceramic microwave absorbing material prepared by this invention is attributable to the preparation method described in this invention and is unrelated to the intrinsic microwave absorption performance of the original foam ceramic.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-temperature resistant foam ceramic microwave absorbing material, characterized in that, Includes the following steps: (1) Mix silicon carbide powder and calcium carbonate powder evenly to form a mixed powder; (2) Mix the mixed powder obtained in step (1), borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose and water, stir evenly to make a slurry; (3) Immerse the foam ceramic component made of foam ceramic in the slurry obtained in step (2), draw a vacuum to reduce the air pressure on the surface of the slurry, and then restore the air pressure on the surface of the slurry to normal pressure. (4) Dry the foam ceramic component obtained in step (3); (5) Sinter the foam ceramic component obtained in step (4). During the sintering process, sinter at 935~950℃ for 16~19min to obtain the high temperature resistant foam ceramic microwave absorbing material.

2. The method for preparing the high-temperature resistant foam ceramic microwave absorbing material according to claim 1, characterized in that, In step (1), the weight ratio of silicon carbide powder to calcium carbonate powder is 1:(1.5~2.2).

3. The method for preparing the high-temperature resistant foam ceramic microwave absorbing material according to claim 1, characterized in that, In step (2), the weight ratio of the mixed powder, borax, sodium silicate, potassium carbonate, polyvinyl alcohol, sodium carboxymethyl cellulose and water is (5.3~7.9):(1.2~1.4):(14~16):(1.2~1.5):(0.2~0.3):(0.3~0.5):

100.

4. The method for preparing the high-temperature resistant foam ceramic microwave absorbing material according to claim 1, characterized in that, In step (3), vacuuming is performed to reduce the air pressure on the surface of the slurry to 0.71~0.79 standard atmospheres and maintain this pressure for 9~13 minutes.

5. The method for preparing the high-temperature resistant foam ceramic microwave absorbing material according to claim 4, characterized in that, In step (3), the air pressure on the surface of the slurry is restored to normal pressure and maintained for 3-5 minutes.

6. The method for preparing the high-temperature resistant foam ceramic microwave absorbing material according to claim 1, characterized in that, In step (4), during the drying process, the temperature is kept at 85~90℃ for 120~150 minutes.

7. The method for preparing the high-temperature resistant foam ceramic microwave absorbing material according to claim 1, characterized in that, In step (1), the average particle size of silicon carbide powder is 10~20μm.

8. The method for preparing the high-temperature resistant foam ceramic microwave absorbing material according to claim 1, characterized in that, In step (1), the average particle size of calcium carbonate powder is 5~10μm.

9. A high-temperature resistant foam ceramic microwave absorbing material, made by the preparation method of the high-temperature resistant foam ceramic microwave absorbing material as described in any one of claims 1 to 8.

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